The overarching goal of this study is to establish a large offspring cohort to investigate the long-term intergenerational impacts of GDM and obesity on the metabolic, vascular, and reproductive health of the offspring. The proposed data collection will also create opportunities to evaluate many other health outcomes, such as neurodevelopment, kidney function, immune function, bone development, etc. In the present study, we will apply a hybrid design which combines maternal and offspring data that have been prospectively and longitudinally collected with newly collected data. This study will leverage two ongoing mother-offspring cohorts, the Nurses Health Study II (NHS-II; mothers) and the Growing Up Today Study (GUTS; offspring) in the United States (herein referred to as the Harvard School of Public Health, HSPH, site) and the mother-offspring pairs in the Danish National Birth Cohort (DNBC) in Denmark collected over more than 20 years and covering a lifespan from pre-conception through young adulthood, augmented with new collection of data and biological specimens. The current study aims to collect data at a single time point on 4,700 offspring, their parents, and 200 of their siblings. Offspring will be oversampled on the exposures of GDM and overweight/obesity in utero. Specifically, 1510 offspring born to a mother with a GDM affected pregnancy, 705 offspring born to a mother who was obese (BMI30 kg/m2) during pregnancy without GDM, 705 offspring born to an overweight (30>BMI25 kg/m2) mother without GDM, 1780 offspring born to a normal weight mother without GDM, and 200 offspring siblings born to a mother with pregnancies discordant for GDM. For participants from the HSPH site, data collection includes online questionnaires and at-home biospecimen collection kits (for all offspring and mothers). For participants from the DNBC site, one-time clinic visits will be conducted which includes online questionnaires, biospecimen collection, physical exams and clinical tests (for all offspring and a subgroup of 520 mothers). Questionnaires and biospecimen collection will be tailored to the age groups and sex of the participant. Biological fathers of participating offspring at both sites will also be asked to complete an online questionnaire.